The 11/11 dupe, also known as the Jump Dupe, was a massive duplication glitch on the server that occurred on November, 11th, 2016. The easy way to duplicate items was leaked to the 2b2t community by RusherIsAutistic, causing mass duping across the entire server. This was the largest duplication glitch that the server had ever seen before then since you could dupe your entire inventory at once. The dupe involved tossing an item out and instantly disconnecting the server. When you logged back in, your item on the ground and in your inventory.
On 11/19, a client by Kinorana made to make duping easier was spread among the community. You would be able to drop your entire inventory on the ground at once and automatically instantly disconnect. You could now dupe your entire inventory at once. However, the client was actually backdoored, and people who duped using the client had their stashes leaked on the 2b2t Reddit. This did not stop players, as there were other clients to use such as Impact and Wurst. The 11/11 dupe ended shortly after 2b2t was updated to 1.11 on 11/28.
However, a specific group of players, members of the 4th Reich had another way to duplicate. This was the first method used before other client's were made consisting of other types of kicks which could be used. This method involved using two Minecraft windows which you would login to one and drop an item before being kicked on the other.
The 11/11 Dupe caused the amount of items in the server to overflow, with most players having double chests of God Apples and other rare items. This basically caused the 2b2t economy to crash and items from the dupe are still in mass circulation today.